<!DOCTYPE html>
<html>
    <head>
        <title>PC端页面</title>
        <!--  1. 设置视口 -->
        <meta name="viewport" content="width=device-width, initial-scale=1.0,user-scalable=no,
        maximum-scale=1.0,minimum-scale=1.0
        ">
        <style>
            .main{
                /* font-size:30px; */
                font-size:50px;
            }
            span{
                font-size:2em;
            }
        </style>
       
    </head>
    <body>
        <!-- 
            默认浏览器的字体大小是16px
            em 是相对 父元素 的字体大小

         -->
        <div class="main">
            <span>
                😊👍💯
            </span>
        </div>
    </body>
</html>